Incorrect IP address on roaming clients

I have a network of about 30 ap1220b access points. Each is on a seperate subnet with an associated DHCP server. Everything was working perfectly for several years until I replaced one ap1220b with an ap1231g. Clients have no problem connecting to any of the APs but some clients (cisco 350 cards) will keep the IP address assigned through the ap1231g when they roam to a ap1220b. The clients can roam from ap1220b to ap1220b without problem and from ap1220b to ap1231g without problem. The only problem is going from the ap1231g to a ap1220b.